Assay for diagnosing streptococcus pneumoniae

ABSTRACT

Assays for detecting anti-streptococcal antibodies in biological samples using one or more streptococcal antigens are described herein. Various combinations of antigens may be used in the assays. For example, one or more of Ply, PhtD, PhtE, LytB and PcpA may be utilized. Additional streptococcal antigens may also be used. The assays may also be used in combination with assays that detect streptococcal nucleic acids.

RELATED APPLICATIONS

This application claims priority to U.S. Ser. No. 61/063,376 filed Feb. 1, 2008.

FIELD OF THE DISCLOSURE

Described herein are reagents and methods for diagnosing bacterial infections.

BACKGROUND OF THE DISCLOSURE

Community-acquired pneumonia (CAP) is one of the most common pediatric infections, a major cause of morbidity in industrialized countries, and a leading cause of mortality worldwide in children under five years of age (Mulholland K, Lancet 2007; 370(9583): 285-9); Pio A, BWHO; 2003; 81(4):298-300). CAP may be caused by multiple agents alone or in combination, including respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Chlamydia and Mycoplasma pneumoniae (Yin C C Respirology, 2003; 8(1):83-9; Chiang W C Respirology 2007; 12(2):254-61; Juven T PIDJ 2000; 19(4): 293-8). Etiological diagnosis is particularly challenging in young children, in whom blood cultures usually remain negative, bronchial secretions are rarely accessible, and frequent nasopharyngeal carriage limits the usefulness of microbial detection. Increasing the number of assays for pathogen detection nevertheless enhances the likelihood of the identification of a causal agent (Wang Pediatr Pulmonol 2008 feb 43(2)150-9; Nakayama E J Infect Chemother 2007, 13(5):305-13), and recent studies using modern diagnostic tools have repeatedly identified S. pneumoniae as a leading cause of CAP, both in primary-care, and in hospital settings (Juven T PIDJ 2000; 19(4): 293-8; Michelow I C; Pediatrics 2004; 113(4):701-7).

Protection against pneumococcal infection is essentially mediated by antibodies promoting opsonophagocytosis. Such antibodies may be directed against pneumococcal polysaccharides (PPS) or pneumococcal surface proteins (PSP). In the absence of pneumococcal immunization, such antibodies are elicited by pneumococcal exposure, colonization and/or infections. The lack of protective antibodies against pneumococcal antigens is thus at the basis of the vulnerability of infants and young children to pneumococcal disease. Although certain PSPs have been used in the serological diagnosis of pneumococcal infections, with excellent specificities and positive predictive values, such studies have frequently been limited by a low sensitivity in children. This was largely attributed to higher colonization prevalence interfering with serological analyses (Scott, et al. Clin. Diagn. Lab. Immunol. 2005).

The etiological diagnosis of pneumococcal pneumonia remains challenging, particularly in young children. Microbial diagnosis based on blood culture or DNA amplification has a high specificity but a low sensitivity in children who are rarely bacteremic. In contrast, high rates of nasopharyngeal colonization limits the sensitivity of assays detecting bacteria and/of fragments thereof in nasopharynx or urine samples (Dowell, S. F., Clin. Infect. Dis. 2000 32:824-825). The quest for a robust methodology of serological diagnosis of pneumococcal pneumonia has been met with many difficulties (Kanclerski, J Clin Microbiol 1988; Korppi M, Eur J Clin Microbiol Infect Dis 2007).

Diagnosis of community-acquired pneumonia (CAP) is particularly challenging in young children through traditional laboratory methods. There is a need in the field for reagents and methods useful for accurately and quickly diagnosing CAP, especially in young children. This need relates to both individual diagnosis, which requires assays providing rapid results with high sensitivities and negative predictive values to avoid useless antibiotic administration, and in epidemiological studies requiring assays with high specificity and positive predictive values for optimal case definition and adequate sensitivity to correctly estimate disease burden. Reagents and methods for accurately and quickly diagnosing CAP are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Anti-PSP serum IgG antibodies at admission.

FIG. 2. Distribution of anti-PhtD IgG antibodies in children with pneumococcal or non-pneumococcal CAP.

FIG. 3. Distribution of anti-PhtE IgG antibodies in children with pneumococcal or non-pneumococcal CAP.

FIG. 4. Distribution of anti-Ply IgG antibodies in children with pneumococcal or non-pneumococcal CAP.

FIG. 5. Distribution of anti-PcPA IgG antibodies in children with pneumococcal or non-pneumococcal CAP.

SUMMARY OF THE DISCLOSURE

Assays for detecting anti-streptococcal antibodies in biological samples using one or more streptococcal antigens are described herein. Various antigens alone or combinations of antigens may be used in these assays. For instance, the assay may be performed to detect antibodies immunoreactive to Ply and one or more of PhtD, PhtE, LytB and PcpA; PhtD and one or more of Ply, PhtE, LytB and PcpA; PhtE and one or more of Ply, PhtD, LytB and PcpA; LytB and one or more of Ply, PhtD, PhtE, and PcpA; and/or PcpA and one or more of Ply, PhtD, PhtE, and LytB. The assays described herein may also be used with other streptococcal antigens in combination with one another and/or one or more of Ply, PhtD, PhtE, LytB, and/or PcpA. In this manner, sensitivity of the assay is increased and the negative predictive value is improved.

DETAILED DESCRIPTION

Provided herein are reagents and methods for accurately and quickly diagnosing community-acquired pneumonia (CAP) are described herein. The assays described herein overcome the low sensitivity of pneumococcal surface protein (PSP)-based immunoassays in children due to the traditional use of only one or a few immunogenic pneumococcal antigens. By detecting antibodies to a combination of bacterial antigens in the serum or other biological fluid of patient, a CAP diagnosis may be made. As shown herein, multiple PSPs were utilized as immunological probes to assess the pattern of humoral immunity driven by past exposure and acute pneumococcal infection in young children hospitalized for CAP. In one embodiment, the antigens may be selected from pneumolysin (Ply), PhtD, PhtE, LytB, and/or PcpA. The sequences of these five pneumococcal surface proteins are widely conserved across pneumococcal strains (>95-98%), allowing their use as markers of exposure to S. pneumoniae as well as vaccine candidates.

Pneumolysin (Ply) is a cytolytic-activating toxin implicated in multiple steps of pneumococcal pathogenesis, including the inhibition of ciliary beating and the disruption of tight junctions between epithelial cells (Hirst et al. Clinical and Experimental Immunology (2004)). Several pneumolysins are known and would be suitable in practicing the assays described herein including, for example GenBank Accession Nos. Q04IN8, P0C2J9, Q7ZAK5, and ABO21381, among others. In one embodiment, Ply has the amino acid sequence shown in SEQ ID NO.: 1.

PhtD polypeptides suitable for practicing the assays described herein include, for example, those of GenBank Accession Nos. AAK06760, YP816370 and NP358501, among others. In one embodiment, PhtD has the amino acid sequence shown in SEQ ID NO.: 2.

PhtE polypeptides suitable for practicing the assays described herein include, for example, those of GenBank Accession Nos. AAK06761, YP816371 and NP358502, among others. In one embodiment, PhtE has the amino acid sequence shown in SEQ ID NO.: 3.

LytB polypeptides suitable for practicing the assays described herein include, for example, those of GenBank Accession Nos. CAA09078, YP816335, ABJ55408, AAK19156, NP358461, and AAK75086, among others. In one embodiment, LytB has the amino acid sequence shown in SEQ ID NOS.: 4, 5 or 8.

PcpA was first cloned and characterized in 1998 as a choline-binding protein with a putative adhesion role (Sanchez-Beato A FEMS Microbiology Letters 164 (1998) 207-214). PcpA polypeptides suitable for practicing the assays described herein include, for example, those of GenBank Accession Nos. CAB04758, YP817353, AAK76194, NP359536, ZP01835022, and ZP01833419, among others. In one embodiment, PcpA has the amino acid sequence shown in SEQ ID NOS.: 6 or 7.

The antigens may be used in the assays described herein, either alone or in combination with one another. The use of single antigens or any combination of antigens may be suitable for use in the assays described herein provided the assay demonstrates the desired sensitivity and negative predictive values. In certain embodiments, the use of a combination of antigens may result in a sensitivity of approximately, 0.80, 0.85, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.0 with a negative predictive value of approximately 0.80, 0.85, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.0. In some embodiments, the values are significant. Comparisons may be performed and significance determined using any of the available statistical analysis tools, alone or in combination with one another, including, for example, student's T-test, chi-square test, Fisher's exact test, analysis of variance (ANOVA), univariate statistical analyses, logistic regression analysis to calculate adjusted odds ratio (OR) and 95% confidence interval (CI). Conrols for any statistically significant demographic variables that might function as confounders (gender, etc) may also be utilized. Differences between values are typically considered significant at p<0.05 or p<0.01, for example. Other statistical analysis tools may also be used.

For instance, the assays may be performed to detect antibodies immunoreactive to only one of Ply, PhtD, PhtE, LytB or PcpA, without assaying for antibodies reactive to any other antigen. Alternatively, the assay may be performed to detect antibodies immunoreactive to more than one of Ply, PhtD, PhtE, LytB and/or PcpA. For instance, the assay may be performed to detect antibodies immunoreactive to Ply and one or more of PhtD, PhtE, LytB and PcpA; PhtD and one or more of Ply, PhtE, LytB and PcpA; PhtE and one or more of Ply, PhtD, LytB and PcpA; LytB and one or more of Ply, PhtD, PhtE, and PcpA; and/or PcpA and one or more of Ply, PhtD, PhtE, and LytB. The assay may also be performed to identify antibodies immunoreactive to combinations of antigens such as PcpA and Ply; PcpA and PhtD; PcpA and PhtE; PcpA and LytB; PcpA, Ply, and PhtD; PcpA, Ply, PhtD, and PhtE; Ply, PhtD, PhtE, and LytB; PcpA, PhtD, and PhtE; PcpA, PhtD, PhtE, and LytB; PcpA, PhtE, and LytB; PcpA, Ply, PhtE, and LytB; PcpA, PhtD, and LytB; PcpA, Ply, and LytB; PcpA, Ply, PhtD, and LytB; PcpA, Ply, and PhtE; and/or, PcpA, PhtD, and PhtE. Other combinations will be apparent to one of skill in the art given this disclosure. The assays described herein may also be used with other streptococcal antigens in combination with one another and/or one or more of Ply, PhtD, PhtE, LytB, and/or PcpA.

In certain embodiments, an isolated and purified PcpA protein or immunologically reactive fragment thereof may be used for detecting a past infection or active infection by Streptococcus pneumoniae in a subject by detecting the binding of antibodies in a sample obtained from a subject to said isolated and purified PcpA antigen (e.g., protein or immunologically reactive fragment thereof). In other embodiments, the isolated and purified PcpA antigen may be used with at least one additional antigen (e.g, PhtD, PhtE, LytB and/or Ply protein or immunologically reactive fragment thereof). Thus, a method of detect the presence of and/or diagnosing pneumoniae or infection by S. pneumoniae in a subject comprising detecting in a biological sample from said subject antibodies against one or more PcpA, PhtD, PhtE, LytB, and/or Ply antigens, wherein the presence of antibodies that bind to the antigen(s) is indicative of infection, is provided. In certain embodiments, the method comprises contacting a biological sample derived from a subject with the isolated or purified PcpA, PhtD, PhtE, LytB, and/or Ply antigens of S. pneumoniae for a time and under conditions sufficient for an antigen-antibody complex to form and then detecting the formation of an antigen-antibody complex. Detection of the antigen-antibody complex may be achieved by detecting human immunoglobulin in the complex. In certain embodiments, detection of the antibody may be accomplished by contacting the antigen-antibody complex with a “second” antibody that is immunologically reactive with human immunoglobulin (e.g., anti-human immunoglobulin antibody) for a time and under conditions sufficient for the second antibody to bind to the human immunoglobulin in the complex and then detecting the bound anti-human immunoglobulin. It is preferred that the second antibody is labelled with a detectable marker or reporter molecule.

A method is also provided for determining the response of a subject having pneumonia or an infection by Streptococcus pneumoniae to treatment with a therapeutic compound. The method involves detecting antibodies against a PcpA antigen in a biological sample of the subject after treatment, wherein the amount of antibody detected is increased, unchanged, or decreased as compared to the amount of antibody detectable in a biological sample of the subject obtained prior to treatment, or to that of a normal or healthy subject. In one embodiment, an unchanged or decreased amount of antibody after treatment may indicate that the subject is not responding to treatment. In another embodiment, an unchanged or decreased amount of antibody after treatment may indicate that the subject is responding to treatment. In another embodiment, an increased amount of antibody after treatment may indicate that the subject is not responding to treatment. In another embodiment, an increased amount of antibody after treatment may indicate that the subject is responding to treatment. Treatment regimens may then be adjusted accordingly.

The antigens may be used in these assays as full-length polypeptides. However, the antigens may be related antigens such as, for example, fragments, variants (e.g., allelic, splice variants), orthologs, homologues, and derivatives (e.g., peptides, fusions) that retain reactivity to antibodies found in the biological sample. A fragment, variant, or derivative may have one or more sequence substitutions, deletions, and/or additions as compared to the subject sequence. Fragments or variants may be naturally occurring or artificially constructed. In one embodiment, such related antigens may be prepared from the corresponding nucleic acid molecules. In preferred embodiments, the related antigens may have from 1 to 3, or from 1 to 5, or from 1 to 10, or from 1 to 15, or from 1 to 20, or from 1 to 25, or from 1 to 30, or from 1 to 40, or from 1 to 50, or more than 50 amino acid substitutions, insertions, additions and/or deletions. Related antigens may include peptides, which are typically a series of contiguous amino acid residues having a sequence corresponding to at least a portion of the polypeptide from which it was derived. In preferred embodiments, a peptide may include about 5-10, 10-15, 15-20, 30-20, or 30-50 amino acids.

Substitutions may be conservative, or non-conservative, or any combination thereof. Conservative amino acid modifications to the sequence of an antigen (and/or the corresponding modifications to the encoding nucleotides) may produce a related antigen having functional and chemical characteristics similar to those of parental antigen. For example, a “conservative amino acid substitution” may involve a substitution of a native amino acid residue with a non-native residue such that there is little or no effect on the size, polarity, charge, hydrophobicity, or hydrophilicity of the amino acid residue at that position and, in particlar, does not result altered function of the antigen (e.g., does not cause decreased immunogenicity or reactivity with antibodies in the biological sample). Suitable, exemplary conservative amino acid substitutions are shown below:

Original Preferred Residues Exemplary Substitutions Substitutions Ala Val, Leu, Ile Val Arg Lys, Gln, Asn Lys Asn Gln Gln Asp Glu Glu Cys Ser, Ala Ser Gln Asn Asn Glu Asp Asp Gly Pro, Ala Ala His Asn, Gln, Lys, Arg Arg Ile Leu, Val, Met, Ala, Phe, Norleucine Leu Leu Norleucine, Ile, Val, Met, Ala, Phe Ile Lys Arg, 1,4 Diamino-butyric Acid, Gln, Asn Arg Met Leu, Phe, Ile Leu Phe Leu, Val, Ile, Ala, Tyr Leu Pro Ala Gly Ser Thr, Ala, Cys Thr Thr Ser Ser Trp Tyr, Phe Tyr Tyr Trp, Phe, Thr, Ser Phe Val Ile, Met, Leu, Phe, Ala, Norleucine Leu

Fragments may include antigens with particular regions or domains deleted. It may be beneficial to delete such regions or domains where, for instance, the presence of those regions or domains will interfere with the use of the fragments in the assays described herein. For instance, when using PcpA, Ply, PhtD, PhtE or LytB, the cholinergic binding region may be deleted. An exemplary fragment of PcpA protein is shown in SEQ ID NO.: 7.

In other embodiments, the antigen may include one or more fusion polypeptide segments that assist in purification and/or detection of the antigen. Fusions can be made either at the amino terminus or at the carboxy terminus of the antigen. Fusions may be direct with no linker or adapter molecule or may be through a linker or adapter molecule. A linker or adapter molecule may be one or more amino acid residues, typically from about 20 to about 50 amino acid residues. A linker or adapter molecule may also be designed with a cleavage site for a DNA restriction endonuclease or for a protease to allow for the separation of the fused moieties. It will be appreciated that once constructed, the fused moieties may be derivatized or otherwise manipulated, as is known in the art or according to the methods described herein. Suitable fusion segments include, among others, metal binding domains (e.g., a poly-histidine segment), immunoglobulin binding domains (e.g., Protein A, Protein G, T cell, B cell, Fc receptor, or complement protein antibody-binding domains), sugar binding domains (e.g., a maltose binding domain), and/or a “tag” domains (e.g., at least a portion of α-galactosidase, a strep tag peptide, a T7 tag peptide, a FLAG peptide, or other domains that can be purified using compounds that bind to the domain, such as monoclonal antibodies). This tag is typically fused to the polypeptide upon expression of the polypeptide, and can serve as a means for affinity purification of the sequence of interest polypeptide from the host cell. Affinity purification can be accomplished, for example, by column chromatography using antibodies against the tag as an affinity matrix. Optionally, the tag can subsequently be removed from the purified sequence of interest polypeptide by various means such as using certain peptidases for cleavage.

In certain embodiments, the antigen may be directly or indirectly (e.g., using an antibody) labeled or tagged in a manner which enables it to be detected. An antigen may be directly labeled by attaching the label to the antigen per se. An antigen may be indirectly labeled by attaching a label to a reagent that binds to the antigen, such as an antibody or other moiety. Suitable labels include, for example, fluorochromes such as fluorescein, rhodamine, phycoerythrin, Europium and Texas Red; chromogenic dyes such as diaminobenzidine, radioisotopes; macromolecular colloidal particles or particulate material such as latex beads that are coloured, magnetic or paramagnetic; binding agents such as biotin and digoxigenin; and, biologically or chemically active agents that can directly or indirectly cause detectable signals to be visually observed, electronically detected or otherwise recorded, for example in a FACS, ELISA, western blot, TRFIA, immunohistochemistry, evanescence, Luminex bead array, dipstick, or other lateral flow assay format. Suitable antibody-binding molecules for use in such methods may include immunoglobulin-binding antibodies, for example anti-human antibodies (e.g., anti-human antibodies specific for Ig isotypes or subclasses (e.g., of IgG), or specific for Staphylococcal protein A or G.

Preferred fluorescent tag proteins include those derived from the jelly fish protein known as green fluorescent protein (GFP). Further information on GFP and other fluorophores is given in the following publications: Tsien R Y, “The Green Fluorescent Protein” Annual Reviews of Biochemistry 1998; 67:509-544 Verkhusha, V. and Lukyanov, K. “The Molecular Properties and Applications of Anthoza Fluorescent Proteins and Chromophores” Nature Biotechnology 2004; 22:289-296. Plasmid vectors encoding a wide range of fluorescent tag proteins are commercially available from various suppliers including an array of “Living Colours 8482; Fluorescent Proteins” available commercially from Clontech Laboratories, Inc. Similar vectors can also be obtained from other suppliers including Invitrogen and Amersham Biosciences. Suitable fluorescent proteins derived from GFP are the red-shifted variant EGFP, the cyan shifted variant ECFP and the yellow shifted variant EYFP. EGFP is preferred as the fluorescent marker because it gives bright fluorescence combined with minimal effect on the antigenic properties of the target antigen. Alternative fluorescent marker proteins are commercially available. Biologically or chemically active agents include enzymes, which catalyse reactions that develop or change colours or cause changes in electrical properties, for example, and may also be utilized. They may be molecularly excitable, such that electronic transitions between energy states result in characteristic spectral absorptions or emissions. They may include chemical entities used in conjunction with biosensors. Biotin/avidin or biotin/streptavidin and alkaline phosphatase detection systems may be employed. Further examples include horseradish peroxidase and chemiluminescent reagents. In some embodiments, the non-immobilized antibody-binding molecule or polypeptide may be detected using an antibody which binds to said non-immobilized antibody-binding molecule or polypeptide. A suitable detection antibody may be labeled by means of fluorescence. In some embodiments, the label may be a fluorescent marker (tag) which is used to label the target antigen directly such that the antigen and the fluorescent marker form a fusion protein.

If antibodies against the target antigen are present in a biological sample, the antigen or antibody may be labeled with a tag, and the antigen-antibody complex formed may be detected by, for example, immunoprecipitation. The fluorescence associated with the tag may then be used to determine that protein has been precipitated (qualitative determination) or to determine the amount of protein precipitated (quantitative determination). For example, soluble extracts of a fluorescence-tagged antigen may be incubated with patient sera for an appropriate period of time such as overnight at 4° C. (typically 10-15 μl of serum to 300-500 μl of extract or less) to allow antibodies to bind to the antigen. Protein A or Protein G Sepharose beads, preincubated with low IgG fetal calf serum (Sigma) to block non-specific binding, are then added to the extract/serum mix containing the tagged antigen/antibody complexes, and mixed with gentle rotation for 1 to 2 hours at room temperature. The antibodies within the serum, including those that specifically bind the tagged antigen, are bound by the protein A/G beads. The protein A/G Sepharose beads are then washed in a suitable buffer (typically 10 mM Tris-HCl pH 7.4, 100 mM NaCl/ImM EDTA/1% Triton X-100) to remove any unbound tagged antigen. This may be achieved by multiple (e.g., 2, 3, 4, or 5) rounds of centrifugation, removal of the supernatant, and resuspension in buffer. The beads, some with tagged antigen attached, are then collected and placed in a fluorescence reader, for example a Spectra Max Gemini XS plate reader from Molecular Devices, Inc. The presence of antibodies in the sample may then be quantitated. In the case of GFP, detection may be accomplished using excitation at wavelength 472 nm and emission at 512 nm. The fluorescence excitation will depend upon the fluorophore/tag that is used but it would be possible to combine several different tagged proteins in the same time. For example, one or more of Ply, PhtD, PhtE, LytB and/or PcpA may be separately tagged and separately or simultaneously assayed. The sensitivity of the method is dependent on the detection device and can be considerably enhanced by using more sensitive detection devices. Various modifications of these methods could also be utilized. Other labels are available in the art and may be suitable for use the assays described herein.

The assays described herein for detecting antibodies immunoreactive with streptococcal antigens may also be combined with other assays useful for detecting streptococcal infection. For instance, these assays (i.e., ELISA) may be combined with polymerase chain reaction (PCR) assays for detecting streptococcal nucleic acid in a biological sample. Alternatively, an ELISA assay may be combined with an immunoprecipitation assay. Or, a PCR-based assay may be combined with an immunoprecipitation assay. Combining the various assays described herein may serve to even further increase the sensitivity of detection and further decrease the negative predictive value of the data.

Also provided herein as kits for detecting the presence of streptococcus infection in a patient by detecting antibodies or nucleic acid in a biological sample of the patient. In one embodiment, one or more pneumococcal antigens (i.e., Ply, PhtD, PhtE, LytB, and/or PcpA) may form part of a kit for detecting or diagnosing anti-streptococcal antibodies in a biological sample. The antigens may be provided in a suitable container such as a vial in which the contents are protected from the external environment. Thus, a kit for detecting an anti-streptococcal antibody in a sample may comprise an antigen (i.e., Ply, PhtD, PhtE, LytB, and/or PcpA) along with one or more detection reagents for determining binding of one or more antibodies in a sample to the antigen is provided. The kit preferably includes: (i) one or more isolated and purified PcpA, PhtD, PhtE, LytB and/or PcpA proteins or immunologically reactive fragments thereof of S. pneumoniae; and (ii) means for detecting the formation of an antigen-antibody complex, optionally packaged with instructions for use.

The antigen(s) may be free in solution or may be immobilized on a solid support, such as a magnetic bead, tube, microplate well, or chip. In certain embodiments, a solid matrix comprising an isolated and purified PcpA, PhtD, PhtE, LytB, and/or PcpA protein or immunologically reactive fragment thereof or a fusion protein or protein aggregate adsorbed thereto is provided. In some embodiments, the kit may further comprise an antibody-binding molecule as a detection reagent. The antibody-binding molecule may be a capture or detection reagent and may be free in solution or may be immobilized on a solid support, such as a magnetic bead, tube, microplate well, or chip. The antibody-binding molecule or polypeptide may be labeled with a detectable label, for example a fluorescent or chromogenic label or a binding moiety such as biotin. Suitable labels are described in more detail above. The kit may further comprise detection reagents such as a substrate, for example a chromogenic, fluorescent or chemiluminescent substrate, which reacts with the label, or with molecules, such as enzyme conjugates, which bind to the label, to produce a signal, and/or reagents for immunoprecipitation (i.e., protein A or protein G reagents). The detection reagents may further comprise buffer solutions, wash solutions, and other useful reagents. The kit may also comprise one or both of an apparatus for handling and/or storing the sample obtained from the individual and an apparatus for obtaining the sample from the individual (i.e., a needle, lancet, and collection tube or vessel). The kit may also include instructions for use of the antigen, e.g. in a method of detecting anti-streptococcal antibodies in a test sample, as described herein. Where the assay is to be combined with another type of assay such as PCR, the required reagents for such an assay (i.e., primers, buffers and the like) along with, optionally, instructions for the use thereof, may also be included.

A better understanding of the present invention and of its many advantages will be had from the following examples, given by way of illustration.

EXAMPLES Example 1 Materials and Methods

Ninety-nine children aged 2 months to 6 years were enrolled in a prospective cohort study at admission for CAP to the pediatric wards of the University Hospitals of Lausanne and Geneva (Switzerland) between March 2003 and December 2005. Children were eligible if presenting with clinical signs of pneumonia according to the WHO classification (ref), children with actively treated asthma, chronic illness or underlying disease, immunosuppression or presenting with wheezing (suspected bronchiolitis) being excluded. None had been immunized against S. pneumoniae, according to the Swiss recommendation in 2003-2005. They were enrolled after signed parental content, as approved by the Ethical Committee of both institutions.

Blood, urine and nasopharyngeal samples were cultivated within 8 hours of admission and assessed for the presence of viruses or bacteria. PCR analyses on nasopharyngeal samples included 13 viruses, Mycoplasma pneumoniae, and Chlamydia pneumoniae, whereas blood samples were assessed by Ply-specific PCR. All chest radiographs taken at admission were reviewed by a senior radiologist blinded to clinical and laboratory findings. Convalescent serum samples were obtained 3 weeks later for 75/99 children who had not been previously immunized against S. pneumoniae. These 75 children were included in this study on CAP-associated anti-pneumococcal responses.

The PhtD, PhtE, PcpA and LytB proteins used in this study are recombinant proteins expressed in E. coli. The PhtD and PhtE used are full-length proteins and the PcpA and LytB used are truncated forms with the choline-binding domain removed. All four proteins are expressed in E. coli as soluble proteins and purified with combinations of ion exchange chromatography. All protein has ≧90% purity after purification as assayed by SDS-PAGE and RP-HPLC.

Paired acute and convalescent serum samples were stored at −20° C. until analysis. Samples were encoded prior to transfer to the laboratory and IgG antibodies to Ply, PhtD, PhtE, PcpA and LytB were measured blindly by laboratory personal unaware of clinical data. Paired serum samples were tested in the same run by indirect ELISA using purified proteins to coat Immulon (Thermo Labsystem) plates. Eight serial dilutions of each serum sample were performed to allow quantification of antibody titers. After 60 min at 37° C., anti-IgG antibody conjugated to horseradish peroxydase (Cappel) was added, followed by ABTS as the substrate. The ELISA titer of each serum was defined by comparison to a reference human AB serum, used in each assay, to which ELISA Units were arbitrarily assigned by taking the reciprocal of its dilution at OD=1.0. Results were expressed in EU/ml. Serum with titers below the assay cut-off of 5 EU/ml were given a titer of 2.5 EU/ml. Antibody titers were log transformed to allow comparisons of mean geometric concentrations (GMC). A significant rise in antibody titers was predefined as a minimal two-fold (100%) increase between the acute- and convalescent-phase samples.

Socio-demographic characteristics of the participants are described using standard descriptive statistics (frequencies, means, geometric means, and standard deviation). Comparison of different serologies were performed using Student's T-test, while categorical data were compared using chi-square tests or Fisher's exact test when appropriate. Serologies among groups were compared by using analysis of variance (ANOVA). Univariate statistical analyses were performed for each variable to determine its relationship to the dependent variable, being a case patient or not. Logistic regression analysis was used to calculate adjusted odds ratio (OR) and 95% confidence interval (CI), controlling for any statistically significant demographic variables that might function as confounders (gender, etc). For all statistical tests, differences were considered significant at p<0.05 or when the 95% CI did not include 1.0. SPSS (version 15.0) statistical-software program was used for analyses.

Example 2 Experimental Results

A. Evidence of Acute Pneumococcal Infection in Children with Cap

Seventy-five previously healthy children (mean age 33.7 months, median 35.4 months, range 2.6 to 66 months, 50% females) were enrolled at admission and provided both acute and convalescent sera for this prospective study of CAP-associated anti-pneumococcal immunity. Only one child had a positive blood culture whereas 15/75 (20%) patients had pneumolysin DNA (Ply⁺-PCR) in their blood. The use of serum IgG seroresponses to Ply (≧2-fold increase between acute and convalescent sera) identified 16/75 (21%) children with evidence of an acute pneumococcal infection (Table 1). This proportion increased to 31% ( 23/75) when combining Ply⁺-PCR and/or anti-Ply seroresponses, which is in accordance with recent reports (reviewed by Korppi M, Eur J Clin Microbiol Infect Dis 2007).

To identify further children with evidence of acute pneumococcal infection, we used four additional PSP (PhtD, PhtE, LytB, and PcpA) as immunological probes to quantify antibody titers in the 75 paired acute and convalescent serum samples. Responses to LytB were rare (Table 1). In contrast, significant (≧2-fold) IgG responses were observed in 21-32% of children hospitalized with CAP (Table 1). Altogether, 34/75 (45%) children had evidence of an acute response to S. pneumoniae. The mean fold-changes in serum IgG antibodies were marked for anti-PhtD (4.22), anti-PhtE (6.88) and anti-PcpA (5.62), moderate for anti-Ply (2.15) and weak for anti-LytB (1.51). Age did not influence the fold change of serum anti-PSP antibodies (R²<0.162 for each PSP), indicating that even young infants may raise anti-PSP responses to acute pneumococcal infection. This was confirmed by the observation of three 8-10 months old infants with marked seroresponses (mean 2.88-6.82 fold changes) to PhtD, PhtE, and PcpA. Last, seroresponses were frequently directed against several PSP (≧2 PSP: 30%, ≧3 PSP: 25%, ≧4 PSP: 14%, ≧5 PSP: 1%), providing strong evidence of recent pneumococcal exposure.

The 34/75 (45%) children with acute seroresponses to ≧1 PSP included 86% ( 13/15) Ply⁺-PCR patients. Only 2 Ply⁺-PCR children lacked anti-PSP response: a 2.6-month-old boy, presumably too young to rapidly raise infection-driven B cell responses, and a 43-month-old girl admitted with a 17-days history of cough, and 7 days of fever, who already had high acute serum titers against the 5 PSP when eventually admitted with lobar pneumonia. Thus, combining Ply⁺-PCR and seroresponses to a panel of 5 PSP identified 36/75 (48%) children hospitalized for CAP as with strong evidence of acute pneumococcal infection (P-CAP).

B. Immunoprobes for the Diagnosis of Pneumococcal CAP in Young Children

The 36 CAP children with evidence of acute pneumococcal responses (≧2-fold rise) and/or infection (Ply⁺-PCR) (P-CAP) to 31 children with no evidence of recent pneumococcal exposure (negative Ply PCR and lack of a ≧2-fold rise of IgG titer to any PSP (NP-CAP) were studied. Eight children with very high (>300 EU/ml) admission serum titers against ≧3 PSP were excluded from these analyses to avoid attribution errors, as high anti-PSP may reflect recent exposure or infection while limiting the likelihood of a ≧2-fold response. Such an approach sets the assay's specificity and positive predictive value at 1.00, as responders are by definition not included in the control group. However, it allows comparing assay sensitivity and negative predictive values in well-controlled study groups. Relying on Ply⁺-PCR alone to diagnose pneumococcal CAP would have missed 19/36 (53%) patients, in accordance with the fact that pneumococcal pneumonia is seldom bacteremic. The use of anti-Ply IgG responses alone would have missed 17/36 (47%) children, yielding a sensitivity of 0.44 and a negative predictive value of 0.61 that are also in accordance with previous reports (Table 1). Higher values resulted from the use of either anti-PhtE or anti-PcpA alone (Table 1). As postulated, combining several PSPs further increased assay sensitivity (Table 2). The combination of anti-PcpA and anti-PhtE responses resulted in a sensitivity of 0.92, with a negative predictive value of 0.91. These values were further increased by adding anti-Ply responses, the combination of anti-PcpA, PhtE and Ply responses yielding the optimal result of 0.94 for both sensitivity and negative predictive values. Importantly, the maximal sensitivity of any combination of PSP that does not include PcpA remained below 0.68. This confirms that increasing the number of antigens enhances the likelihood of the identification of a causal agent of CAP, and that certain immunoprobes more significantly contribute to the diagnosis of pediatric pneumococcal CAP than others.

C. Clinical Characteristics of Children with Pneumococcal or Non-Pneumococcal CAP

It was then of interest to determine whether children with strong evidence of acute pneumococcal infection (P-CAP, n=36) differed in their demographic or clinical characteristics from children (n=31, NP-CAP) without evidence of recent pneumococcal exposure. Univariate analyses indicated that neither age (33.5 vs 32.7 months), gender (50% vs 48% females), clinical severity of pneumonia (WHO score I: 5 vs 1, II: 23 vs 21, III: 7 vs 9), duration of cough (7 vs 4 days), duration of fever (4.2 vs 3.2 days) nor antibiotic use within 30 days of admission (9 vs 8 children) differed in children hospitalized for P-CAP or NP-CAP. This confirms that clinical patterns alone may not reliably identify children with CAP of pneumococcal origin.

D. Distinct Pneumococcal Immunity in Children Admitted for Pneumococcal or Non-Pneumococcal CAP

Given the importance of preexisting anti-pneumococcal antibodies in protection against S. pneumoniae infection, we used a common reference serum to compare PSP-specific immunity at admission and possibly identify differences among P-CAP and NP-CAP children. All 75 patients had detectable serum antibodies to at least one protein and most to several PSP (≧2 PSP: 96%, ≧3 PSP: 92%, ≧4 PSP: 89%, ≧5 PSP: 86%). The highest GMTs were directed against PcpA, Ply and PhtE, while anti-LytB antibodies were significantly lower (Table 3). Antibody titers at admission were markedly heterogeneous. As both pneumococcal exposure and B cell response capacity increase with age, we searched for correlations between age (months) and PSP-specific GMTs (log 10 EU/mL). These correlations were strong for Ply (R²=0.63434), PhtD (R²=0.63297) and PhtE (R²=0.59359) and weaker although significant for LytB (R²=0.45824) and PcpA (R²=0.31625). Assessing exposure-driven anti-PSP antibodies in children distributed in four even age groups (≦17, 18-35, 36-49 and ≧50 months) indicated that anti-PcpA antibodies were already present at high titers in children <18 months (FIG. 1), their further increase with age being significant (p=0.022) but less marked than for other PSPs (p<0.001). Anti-PcpA and anti-PhtE antibodies were already present in the youngest infant, aged 2.6 months, presumably reflecting passive transfer of maternal antibodies.

The five PSP used in this study are well conserved (>95-98%) among pneumococcal strains. Should anti-PSP IgG antibodies play a role in protection against pneumococcal pneumonia, one might therefore expect to find differences in pneumococcal immunity between children with pneumococcal or non-pneumococcal CAP. At admission, antibodies to PhtD, PhtE and LytB were similar in P-CAP and NP-CAP children (Table 4 and FIG. 2), suggesting similar past exposure to S. pneumoniae and B cell response capacity. Anti-Ply at admission were significantly higher in P-CAP (446 EU/ml) than in NP-CAP (169 EU/ml, p=0.03) children. This difference essentially reflected a greater proportion of P-CAP children with high anti-Ply antibodies (>200 EU/ml; FIG. 2) at admission. In striking contrast, anti-PcpA antibodies at admission were 3-fold lower (233 vs 716 EU/ml, p=0.001) in children hospitalized for P-CAP than for NP-CAP, reflecting a greater proportion of NP-CAP children with anti-PcpA titers at any value >10 EU/ml (FIG. 2). Thus, preexisting antipneumococcal immunity differed significantly between children hospitalized with CAP of pneumococcal and non-pneumococcal origin.

Convalescent antibody titers were then compared, harvested 3 weeks after admission for P-CAP or NP-CAP. Convalescent antibody titers to Ply, PhtD, PhtE and Lyt-B remained significantly (p<0.01) influenced by age, which in contrast did not influence anti-PcpA convalescent titers. Anti-LytB antibodies were not increased at all in convalescent sera, indicating the low infection-induced immunogenicity of this antigen (Table 4; FIG. 2). Convalescent antibody titers to the four other PSP were higher in P-CAP than in NP-CAP patients. These differences only reached statistical significance for anti-Ply antibodies (Table 2). This is likely to essentially reflect the marked heterogeneity of seroresponses in relatively small study groups as the reverse distributing cumulative curves clearly indicate the higher proportion of moderate or high anti-PhtD and anti-PhtE titers in P-CAP children (FIG. 2). Interestingly, anti-PcpA antibodies which were 3-fold lower in P-CAP children at admission reached similar titers as in NP-CAP children only 3 weeks after a single episode of pneumonia.

Multivariate analyses confirmed high Ply antibodies (p=0.014) and low PcpA antibodies (p=0.004) at admission as the only significant predictors of pneumococcal versus non-pneumococcal pneumonia in hospitalized children, regardless of their age and clinical scores.

E. Data Analysis

The data demonstrates that the use of a panel of immunogenic PSPs significantly improves the diagnosis of pneumococcal infections in young children with clinical signs of pneumonia, as defined by the World Health Organization (WHO). WHO have identified anti-PcpA antibodies as a key diagnostic marker of pneumococcal CAP. These antibodies are detectable at much lower levels during the acute phase in children with pneumococcal rather than non-pneumococcal pneumonia.

In this study, we postulated that the sensitivity of PSP-based assays could be improved by the use of most immunogenic proteins and/or by their combination. The importance of PSP immunogenicity was largely confirmed by the demonstration of sensitivities ranging from 0.14 for LytB, to 0.44 for Ply, 0.56 for PhtD and 0.64 for either the PhtE or PcpA proteins. This ranking directly reflects the relative immunogenicity of PSP, as evidenced by a similar gradient of mean fold increase of antibody responses (LytB (1.51), Ply (2.15), PhtD (4.22), PcpA (5.62) and PhtE (6.88)) largely independent of age. More impressively, the combination of several PSP markedly increased assay sensitivity: combining anti-PcpA and anti-PhtE responses reached a sensitivity of 0.92 for the diagnosis of a recent pneumococcal exposure/infection in children hospitalized for CAP, which was increased to 0.94 by the addition of anti-Ply responses. One reason for these improved sensitivities, and their related negative predictive values, is that past colonization or infections did usually not elicit antibodies to all PSPs, such that high preexisting antibody titers to one PSP may not prevent responses to other antigens. Another reason is the identification of the PcpA protein as a key diagnostic marker of pneumococcal CAP: in its absence, assay sensitivity reached 0.67 rather than 0.92 regardless of the PSP combination tested (Table 2).

The use of a panel of five PSP as immunoprobes identified 34/75 (45%) CAP children with evidence of acute pneumococcal responses. This included all patients with pneumococcal DNA in their blood (Ply⁺-PCR), with two exceptions: anti-PSP responses remained negative in a less than 3 month-old infant hospitalized after a 4-day history of fever and cough. This suggests that serodiagnosis may remain difficult in very young infants experiencing their first exposure to S. pneumoniae at time of immune immaturity. As few young infants were enrolled in this study, this question will have to be addressed in subsequent studies. The other Ply⁺-PCR child lacking anti-PSP responses was a pre-schooler with a prolonged history of cough (17 days) and fever (7 days) prior to admission for CAP. Her antibody titers were already very high at hospitalization (anti-Ply: 952 EU/ml, anti-PhtD: 192 EU/ml, anti-PhtE: 277 EU/ml, anti-PcpA: 462 EU/ml), indicating their activation prior to admission. To note, the serodiagnosis of this patient would have been considered as positive with less stringent study criteria than the exclusive use of fold-increase of antibody titers. Eight other children (mean age 44.5 months, range 22-66) had high preexisting immunity to ≧3 PSP at admission (anti-Ply>380 EU/ml, anti-PhtD>111 EU/ml, anti-PhtE>393 EU/ml and anti-PcpA>266 EU/ml), and were considered neither as P-CAP nor as NP-CAP patients to avoid attribution errors. Respiratory viruses (RSV, hMPV, parainfluenza, rhinovirus, adenovirus, enterovirus) were identified in all eight except one, who had evidence of M. pneumoniae infection, and all Ply-PCR remained negative. Including these 8 patients to the NP-CAP group would further increase the negative predictive value of each anti-PSP assay.

It cannot be concluded that some anti-PSP responses resulted from nasopharyngeal carriage. At admission, S. pneumoniae was more frequently identified in the nasopharynx of P-CAP than NP-CAP patients (44% versus 22%, p=0.06), in accordance with the fact that nasopharyngeal acquisition precedes pneumococcal disease. For instance, it is known that the acquisition of a new pneumococcal strain induces the development of antibodies to certain PSP such as Ply, PhtB and PhtE (Holmlund E, PIDJ 2007). In contrast, pneumococcal carriage alone is not associated with acute seroresponses. Nasopharyngeal sampling prior to admission for CAP was not available to identify recent acquisition of carriage, and there are reasons to believe that anti-PcpA antibodies are not readily elicited through nasopharyngeal carriage acquisition (see below). AOM was diagnosed at admission in three NP-CAP and four P-CAP patients (NS), antibiotic prescription within 30 days being similar in both groups. Previous prospective studies on the etiology of CAP did not include formal control groups of healthy children or of patients suffering from other diseases. Interestingly, admission antibody titers of our 38 CAP patients aged 24-60 months (mean age 43.1 months, P-CAP:18, NP-CAP:18, indeterminate:2) were significantly lower than those of 58 healthy children (mean age 43.6 months) selected as controls with no history of previous lower respiratory tract infection for another study (Ply: 460 vs 745 EU/ml, PhtD: 150 vs 300 EU/ml, PhtE: 382 vs 679 EU/ml, PcpA: 580 vs 1440 EU/ml, respectively). It will thus be interesting to assess the influence of carriage acquisition, AOM and lower respiratory infections on PhtD, PhtE and PcpA immunity in prospective cohort studies.

The etiologic data presented herein corroborates well with findings of other investigators. The attributed role of S. pneumoniae was indeed documented in 44% of cases in a US study with a similar design, study population and extensive diagnostic workup (Michelow 2004). It is also in accordance with the 20-30% protective efficacy of a 7-valent pneumococcal conjugate vaccine. Should the high sensitivity and specificity of these PSP-based immunoprobes be confirmed in other settings, the same could thus prove extremely useful for the evaluation of the pediatric pneumococcal disease burden. Indeed, a pneumococcal etiology may not be solely derived from clinical symptoms, as confirmed again here. Increasing the sensitivity of the diagnosis of pneumococcal CAP would also greatly reduce the size of the studies required to demonstrate pneumococcal vaccine efficacy in various country settings.

It was also observed that anti-pneumococcal immunity at admission was significantly different in children admitted with pneumococcal versus non-pneumococcal CAP. PSP-specific antibodies were found in all children, over a wide range of concentrations reflecting age and past-exposure. Admission antibody levels to PhtD, PhtE and Lyt-B were similar in both groups, supporting the claim that these children were otherwise healthy children who had been previously exposed to S. pneumoniae, with the possible exception of the youngest infants in whom antibodies may have been of maternal origin. At admission, anti-Ply IgG antibodies were ≧2-fold higher in P-CAP children. This significant difference essentially reflected a greater proportion of P-CAP children with high anti-Ply antibodies (>200 EU/ml; FIG. 2) already at admission. Thus, Ply-specific responses were more rapidly induced in children with P-CAP than responses to other PSP. It is tempting to postulate that anti-Ply immunity had been previously induced in these patients, allowing rapid anamnestic responses at time of pneumococcal infection. The observation of higher admission anti-Ply antibodies is in accordance with the findings of others and supports the inclusion of “high” anti-Ply titers in the serologic diagnostic criteria of pneumococcal CAP.

In striking contrast, anti-PcpA antibodies were 3-fold lower in children admitted for pneumococcal CAP, a difference which was highly significant (p=0.001). This is because saliva has the highest in vivo concentration of Mn2+ (36 μM), such that PcpA expression is repressed unless pneumococci invade the lung or bloodstream, where the levels of Mn2+ are 1.000-fold lower (20 nM). As PcpA is not expressed during nasopharyngeal colonization, anti-PcpA responses reflect pneumococcal disease rather than colonization. This may contribute to the unique sensitivity of the PcpA-based assay (Table 3), which avoids confusion with nasopharyngeal-elicited responses. This PcpA expression pattern has another implication: children with preexisting anti-PcpA immunity are those in whom pneumococcal disease has occurred previously. Conversely, low anti-PcpA antibody titers at time of admission for CAP indicate that children may undergo a primary episode of pneumococcal disease—which could be associated with a higher risk of lower respiratory disease. PcpA antibodies may be just a marker of the protective immunity raised by previous disease. In any case, PcpA appears to play a critical role in establishing pneumococcal pneumonia and, therefore, needs to be further assessed as a potential vaccine or diagnostic component.

In summary, a panel of five pneumococcal surface proteins (PSP) was used to identify pneumococcal infection in a prospective study of 75 young children (mean age 33.7 months) hospitalized with CAP. Twenty-three (31%) patients had either a positive pneumolysin (Ply) blood PCR (20%), or a ≧2-fold increase of anti-Ply antibodies (21%). Adding PhtD, PhtE, LytB and PcpA as immunological probes identified 36/75 (45%) patients with acute pneumococcal infection (P-CAP), increasing the sensitivity of the diagnosis from 0.44 (Ply alone) to 0.94. Neither age, gender, WHO scores for clinical severity, duration of cough/fever or prior antibiotic use distinguished these 36 patients from 31 children with no evidence of recent pneumococcal exposure (NP-CAP). At admission, antibodies to PhtD, PhtE and Lyt-B were similar in both groups, whereas anti-Ply antibodies were significantly higher in P-CAP patients than in NP-CAP patients (446 vs 169 EU/ml, respectively; p=0.031). In contrast, P-CAP children had three-fold lower anti-PcpA antibodies (233 vs 716 EU/ml, p=0.001). Multivariate analyses confirmed low PcpA antibodies at time of admission as the most significant predictor (p=0.004) of P-CAP in young children, in accordance with the preferential expression of Pcp A in low Mn²⁺ compartments such as the lung rather than the nasopharynx.

All references cited herein are hereby incorporated by reference in their entirety into this disclosure. While the present invention has been described in terms of the preferred embodiments, it is understood that variations and modifications will occur to those skilled in the art. Therefore, it is intended that the appended claims cover all such equivalent variations that come within the scope of the invention as claimed.

TABLE 1 Convalescent responses to surface pneumococcal proteins Responders (≧2-fold) Mean 95% CI Range (N/%) (EU/ml) (EU/ml) GMT (EU/ml) Sensitivity NPV Ply 16/75 (21%) 895 (389-1401) 154.33 ND-13079 0.44 0.61 PhtD 20/75 (27%) 436 (147-723)  107.48 ND-10287 0.56 0.66 PhtE 24/75 (32%) 978 (302-1654) 241.89 ND-24877 0.64 0.70 LytB 5/75 (7%) 37 (25-49)  23.94 ND-439 0.14 0.50 PcpA 23/74 (31%) 1062 (668-1456) 281.04 ND-10226 0.64 0.70 ND: below detection level; 95% CI: 95% Confidence interval; GMT: geometric mean titers NPV: negative predictive value

TABLE 2 Sensitivities of the combination of anti-PSP responses for the diagnosis of pneumococcal CAP Ply PhtD PhtE PcpA LytB Ply 0.44 0.58 0.67 0.86 0.47 PhtD 0.58 0.56 0.67 0.89 0.61 PhtE 0.67 0.67 0.64 0.92 0.67 PcpA 0.86 0.89 0.92 0.64 0.72 LytB 0.47 0.61 0.67 0.67 0.14

TABLE 3 Exposure-driven serum IgG antibodies to surface pneumococcal proteins Seropositivity* GMT 95% CI Range N/% (EU/ml) (EU/ml) GMT (EU/ml) Ply 67/75 (89%) 498 (233-763) 110.59 ND-8790 PhtD 64/75 (85%) 140 (109-171) 59.94 ND-604 PhtE 71/75 (95%) 326 (249-403) 130.03 ND-1561 LytB 73/75 (97%) 30 (24-36) 21.79 ND-120 PcpA 69/74 (93%) 515 (375-655) 148.36 ND-2563 ND: below detection level; 95% CI: 95% Confidence interval; GMT: geometric mean titers *Defined as ≧5 EU/ml

TABLE 4 Anti-PSP antibodies in children with CAP of pneumococcal versus non-pneumococcal origin NP-CAP (n=31) P-CAP (n=36) P value Mean Mean (P- vs NP- PSP Stage (EU/ml) 95% CI GMT (EU/ml) 95% CI GMT CAP) Ply Acute 169 (86-252) 58.34 446 (220-672)  115.8 0.031 PhtD Acute 125 (80-170) 49.61 112 (74-150) 50.16 0.637 PhtE Acute 291 (190-392)  110.22 264 (161-367)  104.26 0.712 PcpA Acute 716 (442-990)  241.67 233 (138-328)  66.64 0.001 LytB Acute 31 (21-41)  22.16 24 (18-30)  18.61 0.183 Ply Convalescent 165 (86-244) 58.82 1433 (409-2457) 235.13 0.023 PhtD Convalescent 132 (85-179) 49.39 725 (129-1321) 170.54 0.066 PhtE Convalescent 307 (195-419)  105.43 1615 (204-3026) 395.41 0.086 PcpA Convalescent 759 (456-1062) 247.13 1308 (534-2082) 247.98 0.216 LytB Convalescent 28 (20-36)  19.9 42 (17-67)  24.72 0.291 PSP: Pneumococcal surface proteins NP-CAP: Community-Acquired Pneumonia without evidence of acute pneumococcal infection P-CAP: Community-Acquired Pneumonia with evidence of acute pneumococcal infection 95% CI: 95% confidence interval GMT: geometric mean liters 

1. The use of a PcpA antigen for detecting a past infection or active infection by Streptococcus pneumoniae in a subject, wherein said infection is determined by binding of antibodies in a sample obtained from a subject to said PcpA antigen.
 2. The use of a PcpA antigen and at least one additional antigen selected from the group consisting of PhtD, PhtE, LytB and Ply.
 3. The use of claim 2 wherein a combination of antigens are selected from the group consisting of PcpA and Ply; PcpA and PhtD; PcpA and PhtE; PcpA and LytB; PcpA, Ply, and PhtD; PcpA, Ply, PhtD, and PhtE; Ply, PhtD, PhtE, and LytB; PcpA, PhtD, and PhtE; PcpA, PhtD, PhtE, and LytB; PcpA, PhtE, and LytB; PcpA, Ply, PhtE, and LytB; PcpA, PhtD, and LytB; PcpA, Ply, and LytB; PcpA, Ply, PhtD, and LytB; PcpA, Ply, and PhtE; and, PcpA, PhtD, and PhtE.
 4. A method of diagnosing pneumonia or an infection by Streptococcus pneumoniae in a subject comprising detecting in a biological sample from said subject antibodies against a PcpA antigen wherein the presence of said antibodies in the sample is indicative of infection.
 5. The method of claim 4 additionally comprising detecting antibodies against at least one additional antigen selected from the group consisting of PhtD, PhtE, LytB and Ply, or one or more immunologically reactive fragments thereof.
 6. The method of claim 5 wherein the antigens are selected from the group consisting of PcpA and Ply; PcpA and PhtD; PcpA and PhtE; PcpA and LytB; PcpA, Ply, and PhtD; PcpA, Ply, PhtD, and PhtE; Ply, PhtD, PhtE, and LytB; PcpA, PhtD, and PhtE; PcpA, PhtD, PhtE, and LytB; PcpA, PhtE, and LytB; PcpA, Ply, PhtE, and LytB; PcpA, PhtD, and LytB; PcpA, Ply, and LytB; PcpA, Ply, PhtD, and LytB; PcpA, Ply, and PhtE; and, PcpA, PhtD, and PhtE.
 7. The method of any one of claims 4-6 comprising contacting a biological sample derived from the subject with the antigen for a time and under conditions sufficient for an antigen-antibody complex to form and then detecting the formation of an antigen-antibody complex.
 8. The method of claim 7 wherein detecting the formation of an antigen-antibody complex comprises detecting human immunoglobulin in the antigen-antibody complex.
 9. The method of claim 8 wherein detecting human immunoglobulin comprises contacting the antigen-antibody complex with a second antibody that binds to human immunoglobulin for a time and under conditions sufficient for said second antibody to bind to the human immunoglobulin in the complex and then detecting the bound anti-human immunoglobulin.
 10. The method of claim 8 wherein the second antibody is labeled with a detectable marker or reporter molecule.
 11. A method for determining the response of a subject having pneumonia or an infection by Streptococcus pneumoniae to treatment with a therapeutic compound for said pneumonia or infection, said method comprising detecting antibodies against a PcpA antigen in a biological sample of the subject after treatment, wherein the amount of antibody detected is increased, unchanged, or decreased compared to the amount of antibody detectable in a biological sample of the subject obtained prior to treatment or that of a normal or healthy subject, wherein an unchanged or decreased amount of antibody after treatment indicates that the subject is not responding to treatment.
 12. The method of claim 11 comprising detecting antibodies immunoreactive with at least one antigen selected from the group consisting of PhtD, PhtE, LytB and Ply.
 13. The method of any one of claim 11 or 12 comprising contacting the biological sample with the antigen for a time and under conditions sufficient for an antigen-antibody complex to form and then detecting the formation of an antigen-antibody complex.
 14. The method of claim 13 wherein detecting the formation of an antigen-antibody complex comprises detecting human immunoglobulin in the antigen-antibody complex.
 15. The method of claim 14 wherein detecting human immunoglobulin comprises contacting the antigen-antibody complex with a second antibody that binds to human immunoglobulin for a time and under conditions sufficient for said second antibody to bind to the human immunoglobulin in the complex and then detecting the bound anti-human immunoglobulin.
 16. The method of claim 15 wherein the second antibody is labeled with a detectable marker or reporter molecule.
 17. The method of one of claim 7 or 13 comprising performing an enzyme-linked immunosorbent assay (ELISA).
 18. The method of claim 17 wherein the ELISA is a sandwich ELISA using a capture antibody and a detection antibody.
 19. A kit for detecting Streptococcus pneumoniae infection in a biological sample, the kit comprising: (i) the isolated and purified PcpA antigen; and, (ii) reagents for detecting the formation of an antigen-antibody complex.
 20. The kit of claim 19 further comprising instructions for use.
 21. The method of any one of claims 4-18 further comprising detecting Streptococcus pneumoniae nucleic acid in the biological sample.
 22. The method of claim 21 wherein the nucleic acid corresponds to a nucleic acid encoding the PcpA protein.
 23. A solid matrix comprising an antigen selected from the group consisting of PcpA, Ply, PhtD, PhtE, and LytB adsorbed thereto.
 24. A solid matrix comprising a combination of isolated and purified antigens adsorbed thereto, said combination being selected from the group consisting of PcpA and Ply; PcpA and PhtD; PcpA and PhtE; PcpA and LytB; PcpA, Ply, and PhtD; PcpA, Ply, PhtD, and PhtE; Ply, PhtD, PhtE, and LytB; PcpA, PhtD, and PhtE; PcpA, PhtD, PhtE, and LytB; PcpA, PhtE, and LytB; PcpA, Ply, PhtE, and LytB; PcpA, PhtD, and LytB; PcpA, Ply, and LytB; PcpA, Ply, PhtD, and LytB; PcpA, Ply, and PhtE; and, PcpA, PhtD, and PhtE.
 25. The solid matrix of claim 23 or 24 wherein the solid matrix is selected from the group consisting of a microtiter plate or a microarray.
 26. A method of diagnosing infection by Streptococcus pneumoniae comprising contacting a biological sample with a solid matrix of any one of claim 23, 24 or 25 under conditions suitable for an antibody reactive to one or more of the antigens to bind thereto, and detecting the binding of said antibody to at least one or none of said antigens. 